The Principal Investigator has isolated a new hormone-like peptide called chymodenin from porcine duodenum which exhibits unique biological activity; the selective and perhaps exclusive enhancement of chymotrypsinogen secretion relative to other digestive enzymes by the pancreas. Chymodenin produces a dramatic increase in chymotrypsinogen secretion by the pancreas, the increase is accompanied by non-parallel fashion by a modest increase in total protein output, and no increase in the basal lipase output rate. Chymodenin's effects are unique - in that other pancreatic secretory stimulants give a massive non-selective increase in the output of pancreatic proteins. Since chymodenin's effect does not appear to be due solely to increased enzyme synthesis because of the rapid response, and since the secretion does not contain elevated levels of all enzymes, the secretory mechanism appears to be unique. The broad objectives of this proposal are to study chymodenin's hormonal status - is it a new gastrointestinal hormone?, and to examine in detail its mechanism of action. We will determine its amino acid sequence, and major chemical characteristics including the role of the disulfide bridge, develop a radioimmunoassay and bioassay for the new molecule, and investigate its release from the intestinal wall using the radioimmunoassay to follow its secretion into the blood stream.